parse method

The source must be either a non-empty sequence of base-radix digits,
optionally prefixed with a minus or plus sign ('-' or '+').

The radix must be in the range 2..36. The digits used are
first the decimal digits 0..9, and then the letters 'a'..'z' with
values 10 through 35. Also accepts upper-case letters with the same
values as the lower-case ones.

If no radix is given then it defaults to 10. In this case, the source
digits may also start with 0x, in which case the number is interpreted
as a hexadecimal integer literal,
When int is implemented by 64-bit signed integers,
hexadecimal integer literals may represent values larger than
263, in which case the value is parsed as if it is an
unsigned number, and the resulting value is the corresponding
signed integer value.

For any int n and valid radix r, it is guaranteed that
n == int.parse(n.toRadixString(r), radix: r).

If the source does not contain a valid integer literal,
optionally prefixed by a sign, a FormatException is thrown
(unless the deprecated onError parameter is used, see below).

Instead of throwing and immediately catching the FormatException,
instead use tryParse to handle a parsing error.
Example: